SAN FRANCISCO: Facebook director Peter Thiel, who sold more than 16 million shares in the company's initial public offering, has given himself added flexibility to sell more of his holdings, a regulatory filing shows.

Thiel, one of Facebook's earliest investors, converted more than nine million shares to Class A from Class B, according to a document filed August 10 with the US Securities and Exchange Commission.

Thiel, a venture capitalist and hedge-fund manager whose proceeds from the IPO topped $630 million, holds a stake worth more than $550 million. Class A shares are more easily traded publicly, said Erik Gordon, a professor at the Ross School of Business at the University of Michigan.

The status change could add to speculation that big investors - such as Thiel and Goldman Sachs Group - will sell shares when restrictions on sales are lifted . That, plus concern over advertising-sales growth, has dragged down Facebook shares 46% through Wednesday.

"It's certainly not a vote of confidence when a guy who knows as much about it as Peter Thiel knows about it wants to get the rest of his stock into a position so that he can sell it quickly," Gordon said.

Thiel holds more than 27 million Facebook shares and most already carry Class A status, according to regulatory filings.

Other early holders, such as venture capital firm Accel Partners, hold mostly Class A shares. Of those held by Accel and its affiliates, 135.7 million are Class A, while 7.9 million are Class B, according to regulatory filings.

Lockup expiring

Because Class B shares give holders greater voting power than Class A stock, Thiel also is surrendering some of his control over the company. Facebook raised $16 billion on May 17 in the largest-ever technology IPO.

Investors have been shunning the stock on concern over the company's ability to make money from mobile users. The lockup on shares held by investors begins to expire on August 16.

The move by Thiel doesn't necessarily suggest that he's bearish on the company's prospects or that he'll sell immediately, said Michael Pachter, an analyst at Wedbush Securities.

Jonathan Cain, spokesman for Thiel, declined to comment, as did Ashley Zandy, a spokeswoman for Facebook. Facebook, based in Menlo Park, California, fell 5.7% to $20.38 at the close in New York on Wednesday, the biggest decline in two weeks.

Cashing out

Thiel co-founded PayPal and served as chief executive officer until the company was bought by EBay for $1.5 billion in 2002.

Thiel, as a member of the socalled "PayPal Mafia" , used his fortune to start hedge fund Clarium Capital Management and to invest in startups. One of those startups was Facebook , a social-networking service devoted to college campuses at the time of the investment in 2004.

Thiel holds more than 27 million Facebook shares and most already carry Class A status.